Mogawer, Austerman, & Roussel 1 · Dr. Walaa S. Mogawer, P.E. – Corresponding Author . Civil and...

Mogawer, Austerman, & Roussel 1

Performance Characteristics of Asphalt Rubber Mixtures Containing RAP and Warm Mix Asphalt Technology

Dr. Walaa S. Mogawer, P.E. – Corresponding Author

Civil and Environmental Engineering Department Highway Sustainability Research Center (HSRC)

University of Massachusetts Dartmouth 151 Martine Street – Room 124

Fall River, MA 02723 Phone: (508) 910-9824 Fax: (508) 999-9120

Email: [email protected]

Alexander J. Austerman, M.Sc., EIT Highway Sustainability Research Center (HSRC)




Michael Roussel Highway Sustainability Research Center (HSRC)




Submission Date: May 17th, 2011

mailto:[email protected]

mailto:[email protected]


ABSTRACT 1 The purpose of this study was to determine the effect of Reclaimed Asphalt Pavement (RAP) and Warm 2 Mix Asphalt (WMA) technology on the performance of asphalt rubber mixtures. A 12.5mm mixture was 3 designed with an asphalt rubber binder and designated as the control. The same control mixture was then 4 designed incorporating a 25% RAP content Each of the mixture designs (control and 25% RAP) were 5 then repeated at a lower mixing and compaction temperature using a wax-based WMA technology. 6

The mixtures were then evaluated to determine the impact of RAP and WMA technology on the 7 performance of asphalt rubber mixtures in terms of stiffness (dynamic modulus), cracking resistance 8 using the Overlay Test (OT) device, low temperature cracking resistance using the Asphalt Concrete 9 Cracking Device (ACCD), and moisture susceptibility using the Hamburg Wheel Tracking Device 10 (HWTD). 11 Mixture stiffness results indicated that control and 25% RAP mixtures exhibited similar stiffness, 12 both with and without the WMA technology. The OT results indicated that cracking resistance of the 13 mixtures decreased with the addition of RAP. The cracking resistance of the RAP mixture increased 14 slightly with the addition of WMA technology. The low temperature cracking results indicated that the 15 addition of RAP did not increase the potential for low temperature cracking in the mixtures. All of the 16 mixtures tested passed the moisture susceptibility testing in the HWTD. 17 18 BACKGROUND 19 Like crude oil, the price of asphalt binder has been increasing steadily for many years (1). This has led to 20 a continuous trend of price increases for Hot Mix Asphalt (HMA) mixtures. Correspondingly, the HMA 21 industry is continually searching for methods to reduce material costs and maximize their benefits without 22 compromising performance. One such method is to use readily available recycled materials like 23 Reclaimed Asphalt Pavements (RAP) and Crumb Rubber (CR). 24

RAP has been successfully incorporated into HMA since the 1970’s at percentages generally less 25 than 20% by weight of mixture. It can substitute portion of the virgin binder and aggregates required for 26 HMA mixtures. Because less virgin material are used, incorporating RAP in HMA provides cost savings 27 that increase as higher amounts of RAP are used (2). 28

The use of more RAP in HMA is not without concerns as higher amounts can significantly affect 29 the performance of HMA mixtures. As the HMA ages over time, the asphalt binder hardens and oxidizes. 30 Hence, RAP binder is much stiffer binder than a new binder. Depending on the RAP content utilized in 31 HMA, the aged RAP binder can have a pronounced effect on the overall mixture stiffness. This is based 32 on previous research which suggested that aged RAP and new binders will mix (blend) to some extent, 33 thereby changing the properties of the mixtures from one that contains purely new materials (3, 4, 5). 34

In order to combat the changes to HMA mixtures that incorporate RAP, one common approach is 35 to add a rejuvenating additive to the new asphalt binder in order to soften the aged RAP binder in the 36 mixture. If the rejuvenating additive does not adversely impact the performance of the HMA, or better 37 yet improves it, this can allow for higher percentages of RAP to be incorporated into the HMA. This can 38 lead to greater cost savings. Another recycled material, crumb rubber from waste tires, has been reported 39 to assist in delivery of these rejuvenating additives. Instead of adding the rejuvenating additives to the 40 virgin binder, the crumb rubber is used to carry them in the mixture to revitalize the properties of the aged 41 RAP binder. This is due to the absorption properties of the crumb rubber and its overall positive 42 influence on asphalt rheology for these types of mixtures (1). Hence, using crumb rubber in HMA 43 mixtures can permit higher RAP contents to be utilized. 44

Another significant limitation to using large amounts of RAP in HMA is reduced mixture 45 workability. Workability refers to how easily the asphalt mixture can be handled, placed, and compacted. 46 Because high RAP contents contain more aged RAP binder, they will have a more pronounced impact on 47 the overall stiffness of the HMA mixture. Warm Mix Asphalt (WMA) is a new technology that has 48 proven to improve the workability of HMA mixtures including those incorporating RAP (6, 7). In 49 addition to improving workability, WMA technology allows for production and placement of HMA 50


mixtures at lower temperatures than conventional mixtures. These reductions in temperatures allow for 1 the fabrication of more environmentally friendly mixtures since plant and field emissions are reduced. 2

Overall, the use of higher percentage of RAP in asphalt rubber mixtures and a WMA technology 3 has the potential of assisting the industry in designing more cost effective and environmentally friendly 4 asphalt mixtures without jeopardizing performance. The research presented herein focused on designing 5 asphalt rubber mixtures incorporating RAP and WMA technology and comparing their performance to 6 similar mixtures without RAP and WMA technology. Specifically, evaluations and comparisons of 7 mixture stiffness, cracking resistance, low temperature cracking resistance, and moisture susceptibility 8 were conducted. 9 10 Reclaimed Asphalt Pavement (RAP) in HMA 11 RAP is a commonly recycled material that is incorporated in the production of new HMA. It can be 12 generated from full-depth removal or cold milling of an existing HMA layer. Currently, around 75% of 13 all state standard specifications allow at least 10% RAP in the surface course mixtures and allow greater 14 than or equal to 10% in lower pavement lifts. At low RAP contents, below 20%, mixtures have been 15 found to perform as well as virgin mixtures. At high RAP content, greater than 20%, mixtures have 16 exhibited an increase resistance to rutting, but decreased resistance to cracking (thermal and fatigue). 17 This is due to stiffening effect imparted by the aged RAP binder to the blended virgin-RAP binder in the 18 mixture. Hence, it is necessary when using high RAP content to measure the stiffness of the mixture and 19 the mixture resistance to fatigue and low temperature cracking. RAP has also been used as a recycled 20 aggregates base layer. Base layers with RAP have higher strength in comparison to conventional 21 aggregate base (8, 9). 22 23 Asphalt Rubber 24 The processes of incorporating crumb-rubber in HMA can be divided into two broad categories: a dry 25 process and a wet process. In the dry process, crumb rubber is added to the aggregate before the asphalt 26 binder is charged into the mixture. In the wet process, asphalt binder is pre-blended with the rubber at 27 high temperature (177 – 210ºC [351-410ºF]) and specific blending conditions (1). The resultant binder 28 from a wet process is referred to as Asphalt Rubber (AR). According to the American Society for Testing 29 and Materials (ASTM) Specification D 6114 “Standard Specification for Asphalt-Rubber Binder” 30 definition (10) asphalt rubber is “…a blend of asphalt cement, reclaimed tire rubber, and certain additives 31 in which the rubber component is at least 15% by weight of the total blend and has reacted in the hot 32 asphalt cement sufficiently to cause swelling of the rubber particles.” In the study presented herein, an 33 asphalt rubber was used to prepare the mixtures. 34 35 OBJECTIVES 36 This study focused on designing asphalt rubber mixtures incorporating RAP and WMA technology and 37 comparing their performance to similar mixtures without RAP and WMA technology. Specifically, the 38 study objectives were to: 39

1. Design a 12.5mm asphalt rubber mixture with and without a high RAP content and repeat these 40 mixture designs with the addition of a WMA technology. 41

2. Measure the effect on the dynamic modulus (measure of mixture stiffness) of the mixtures due 42 to the high RAP content, WMA technology, and reduced mixing and compaction temperatures associated 43 with the WMA technology. 44

3. Measure the cracking resistance of the mixtures using the Overlay Tester. 45 4. Evaluate the low temperature cracking resistance of the mixtures using a simple performance 46

test known as the Asphalt Concrete Cracking Device (ACCD). 47 5. Measure the moisture susceptibility of the mixtures using the Hamburg Wheel Tracking 48

Device. 49


6. Compare the test data to determine if the asphalt rubber mixtures incorporating RAP and 1 WMA technology perform the same or better than the same mixtures without RAP and WMA 2 technology. 3 4 EXPERIMENTAL PLAN 5 In order to achieve the objectives of this study, an experimental plan was developed as shown in Figure 1. 6 7

12.5mm Asphalt Rubber Mixture

Asphalt Rubber (AR) Binder

Control Mixture

Mixtures Prepared without WMA Technology Mix: 177ºC (351ºF)

Age/Compact: 154ºC (309ºF)

Dynamic Modulus

|E*|

Cracking Resistance

Overlay Tester

Low Temperature Cracking

Asphalt Concrete Cracking Device

(ACCD)

Reclaimed Asphalt Pavement (RAP)

25% RAP Mixture

Control Mixture + WMA

Technology

25% RAP Mixture + WMA

Technology

Performance Testing

Mixtures Prepared with WMA Technology Mix: 160ºC (320ºF)

Age/Compact: 141ºC (286ºF)

WMA Technology

1.0% SonneWarmix

Moisture Susceptibility

Hamburg Wheel Tracking Device

(HWTD)

Virgin Aggregates

8 FIGURE 1 Experimental plan. 9 10 MATERIALS 11 12 Asphalt Rubber Binder 13 An Asphalt Rubber (AR) binder obtained from a regional asphalt supplier was utilized for all mixture 14 designs. This AR binder was fabricated using a PG58-28 base binder incorporating 17% rubber through a 15 wet process. The AR binder conformed to the requirements of ASTM D 6114 Type II specifications (10). 16 Based on the recommendation of the AR binder supplier, the mixing temperature was 177ºC (351ºF) and 17 the compaction temperature was 154ºC (309ºF). 18 19 20


Warm Mix Asphalt Technology 1 To determine if asphalt rubber mixtures incorporating RAP and WMA technology can be produced and 2 compacted at lower temperatures while maintaining the performance characteristics of the control 3 mixtures, a waxed based WMA technology known as SonneWarmix was used. SonneWarmix was being 4 used by the supplier of the asphalt rubber, accordingly it was chosen for this project. This technology was 5 added to the selected mixtures at a dosage rate of 1.0% by weight of total binder (Virgin binder + RAP 6 binder). Mixtures incorporating the WMA were fabricated at lower mixing and compaction temperatures 7 (160ºC [320ºF] and 141ºC [286ºF] respectively) than the conventional mixtures without the technology. 8 9 Aggregates and RAP 10 The virgin aggregates were from a crushed stone source in Wrentham, Massachusetts. Five different 11 aggregate stockpiles were obtained: 12.5 mm crushed stone, 9.5 mm crushed stone, natural sand, stone 12 sand, and stone dust. Each stockpile was tested to determine the aggregate properties in accordance with 13 AASHTO specifications (11). The aggregate properties of each stockpile are shown in Table 1. 14

The RAP was obtained from the same contractor that supplied the virgin aggregates. The binder 15 content of the RAP was determined by the ignition method in accordance with AASHTO T308 (11). The 16 aggregates remaining after ignition were then tested in accordance with AASHTO aggregate test 17 specifications (T11, T27, T84 and T85) in order to determine the gradation and specific gravity of the 18 RAP aggregates. The properties of the RAP are shown in Table 1. 19 20 TABLE 1 Average Virgin Aggregate and RAP Stockpile Properties 21

Sieve Size 12.5mm 9.5mm Natural Sand

Stone Sand

Stone Dust RAP

19.0 mm 100 100 100 100 100 100 12.5 mm 82.8 99.4 100 100 100 93.8 9.5 mm 23.9 93.8 100 10 100 80.2 4.75 mm 1.2 29.7 99.7 99.8 99.7 59.4 2.36 mm 1.1 5.2 98.3 83.7 83.7 46.3 1.18 mm 1.1 2.8 93.3 54.3 57.1 36.4

0.600 mm 1.1 2.3 73.3 33.8 38.6 27.5 0.300 mm 1.1 2.1 29.7 19.0 24.9 17.9 0.150 mm 0.9 1.8 4.8 9.4 15.9 10.8 0.075 mm 0.8 1.5 0.9 4.3 10.9 7.3

Specific Gravity, Gsb (AASHTO T84/T85) 2.641 2.642 2.624 2.644 2.629 2.638

Absorption, % 0.39 0.43 0.45 0.53 0.60 0.76 Binder Content (AASHTO T308) = 4.99%

22 23 MIXTURE DESIGN 24 For this study a 12.5mm Nominal Maximum Aggregate Size (NMAS) control and 25% RAP mixture 25 were developed in accordance with Arizona Department of Transportation (ADOT) materials 26 specification Section 413 “Asphaltic Concrete (Asphalt-Rubber)”(12). The design mixture gradation and 27 combined aggregate properties for each design are shown in Table 2. 28

Mixtures specimens were compacted using the Superpave Gyratory Compactor (SGC) with a 29 compactive effort of 75 gyrations. The gyration level corresponded to a design Equivalent Single Axle 30 Loads (ESALs) of 0.3 to <3 million using the Superpave design methodology. 31

Volumetric specimens were batched, mixed and short-term aged at the compaction temperature 32 for two hours in accordance with AASHTO R30. After aging, specimens (150 mm diameter) were 33


compacted in the Superpave Gyratory Compactor (SGC). The volumetric properties for each mixture are 1 shown in Table 3. 2

3 TABLE 2 Mixture Gradations and Combined Aggregate Properties 4

Sieve Size Control 25% RAP

ADOT Specification Section 413

Asphaltic Concrete (Asphalt Rubber)

ADOT Specification Section 413 Production Tolerance

19.0mm 100 100 100 ±4 12.5 mm 92.6 92.3 80-100 ±4 9.5 mm 65.4 66.2 65-80 ±4 4.75 mm 33.9 33.1 28-42 ±4 2.36 mm 20.3 19.5 14-22 ±3 1.18 mm 13.5 14.2 - - 0.600 mm 9.3 10.4 - - 0.300 mm 6.2 6.9 - - 0.150 mm 4.1 4.3 - - 0.075 mm 2.9 3.0 0-2.5 ±1 Combined Aggregate Specific Gravity

2.640 2.641 2.35-2.85 2.35-2.85

Absorption, % 0.45 0.51 0-2.5% 0-2.5% 5 TABLE 3 Mixture Properties 6

Properties Control 25% RAP ADOT

Section 413 Specification

Total Binder Content, % 8.0 8.0 - Binder from RAP, % 0 1.26

Virgin Binder Added, % 8.0 6.74 - Air Voids,% 5.8 2.6 5.5±1.0%

VMA, % 21.9 19.0 19% min. VFA, % 73.7 86.5 -

Binder Absorbed, % 0.73 0.86 0 -1.0% Dust to Binder Ratio 0.40 0.42 -

Properties Control + 1% WMA

25% RAP + 1% WMA

ADOT Section 413

Specification Total Binder Content, % 8.0 8.0 -

Binder from RAP, % 0 1.26 - Virgin Binder Added, % 8.0 6.74 -

Air Voids,% 5.9 4.7 5.5±1.0% VMA, % 22.0 20.9 19% min. VFA, % 73.3 78.0 -

Binder Absorbed, % 0.73 0.77 0 -1.0% Dust to Binder Ratio 0.40 0.41 -

- Not Applicable 7 VMA = Voids in Mineral Aggregate 8 VFA = Voids Filled with Asphalt 9 WMA = Warm Mix Asphalt Technology (1.0% SonneWarmix by total weight of binder) 10


MIXTURE STIFFNESS - DYNAMIC MODULUS 1 Complex dynamic modulus |E*| testing was conducted to determine changes in mixture stiffness due to 2 the incorporation of RAP and/or the WMA technology. In order to determine the dynamic modulus, test 3 specimens were placed in the Asphalt Mixture Performance Test (AMPT) device and subjected to a 4 sinusoidal (haversine) axial compressive stress at the different temperatures and frequencies. The 5 resultant recoverable axial strain (peak-to-peak) was measured. From this data the dynamic modulus was 6 calculated. 7

Three replicate dynamic modulus specimens were fabricated in the SGC for each mixture. 8 Specimens incorporating WMA technology were produced at the lower mixing and compaction 9 temperatures noted previously. All specimens were aged for four hours at the compaction temperature in 10 a loose state prior to compaction. Each specimen was subsequently prepared for dynamic modulus testing 11 in AMPT in accordance with AASHTO TP62 “Standard Method of Test for Determining Dynamic 12 Modulus of Hot-Mix Asphalt (HMA)”(13) and the draft specification provided in NCHRP Report 614 13 “Proposed Standard Practice for Preparation of Cylindrical Performance Test Specimens Using the 14 Superpave Gyratory Compactor” (14). The final test specimens had an air void level of 7.0 ± 1.0%. Each 15 specimen was tested at temperatures of 4°C, 20°C, and 40°C (39ºF, 68ºF, and 104ºF) and loading 16 frequencies of 10 Hz, 1 Hz, 0.1 Hz, and 0.01 Hz (40°C only) (14). 17

Figure 2 shows the results of the dynamic modulus testing. The error bars shown on the figure 18 indicate the confidence interval for the data. Error bars that overlap indicate the differences in dynamic 19 modulus were not significant. For the mixtures without WMA technology, the dynamic modulus data 20 indicated that the control and 25% RAP mixture exhibited similar stiffness for a majority of the 21 temperatures and frequencies tested with minor variances noted for selected test frequencies at 4º and 22 20ºC (39ºF and 68ºF). Similarly, for mixtures incorporating the WMA technology, the result indicated 23 that the control and 25% mixtures exhibited similar stiffness. Comparing the results for the mixtures with 24 and without the WMA technology indicated that the mixture stiffness significantly decreased for the 25 mixtures incorporating the WMA technology. This is likely a result of less aging due to reduced mixing 26 and compaction (aging) temperatures. Overall, the data confirmed that mixture stiffness was not 27 significantly increased with the addition of up to 25% RAP in the mixture. 28

29


1

10

100

1,000

10,000

4°C - 0.1H

z

4°C - 1.0H

z

4°C - 10H

z

20°C - 0.1H

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20°C - 1.0H

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20°C -10H

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40°C - 0.01H

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40°C - 1.0H

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Control

25% RAP

Control + 1% WMA

25% RAP + 1% WMA

1 FIGURE 2 Comparison of dynamic modulus results. 2 3 CRACKING RESISTANCE TESTING - OVERLAY TEST DEVICE 4 The mixture stiffness increased, although not significantly, due to the incorporation of RAP in the 5 mixtures. Accordingly, each mixture could be mores susceptible to cracking. Therefore all mixtures 6 were tested for their cracking resistance utilizing the Overlay Tester (OT). 7

The OT device was designed to evaluate the cracking potential of asphalt mixtures. The device 8 applies tension loading to test specimens while recording load, displacement, temperature and time (15). 9 Research studies have been conducted that outline the use of this device for evaluation of asphalt mixture 10 cracking susceptibility (16, 17). 11

To evaluate the cracking potential of a mixture, a trimmed gyratory compacted specimen is glued 12 with epoxy onto two plates as shown in Figure 3. The joint between the plates is located at the midpoint 13 of the specimen length. The glued test specimen is placed into the OT device. During testing, one of the 14 plates remains stationary while the other is displaced. The moving plate is pulled, thereby opening the 15 joint between the plates, to a known displacement. The plate is then pushed back to the original location, 16 thereby retuning the joint between the plates to its original position. The opening and closing 17 (displacement) of the joint between the plates occurs in 10 seconds (5 seconds to open the joint and 5 18 seconds to close the joint). Each opening and closing motion is one cycle. During each cycle the load 19 required to move the plates to the specified displacement is recorded. The device is set to terminate the 20 test when the load is reduced a certain percentage from the load recorded for the first cycle or the sample 21 reaches a specific number of cycles without reaching the required load reduction. 22

23


1 FIGURE 3 Specimen setup in Overlay Test (OT) device. 2

3 For this study, the Texas Department of Transportation specification (Tex-248-F) for testing 4

bituminous mixtures with the OT (15) was followed. Specimens without the WMA technology were 5 mixed at 177ºC (351ºF) and then aged four hours at the compaction temperature of 154ºC (309ºF). All 6 specimens containing the WMA technology were mixed at 160ºC (320ºF) and then aged four hours at the 7 compaction temperature of 141ºC (286ºF). Specimens were then fabricated in the SGC and then trimmed. 8 The air void level of the specimens was 7.0±1.0%. 9

All mixtures for this study were tested with a joint opening (displacement) of 0.06 cm (0.025 10 inch), test temperature 15C (59ºF), and a failure criteria of 93% reduction in the load measured during 11 the first cycle or 1,200 cycles (whichever occurs first). The average results of the testing are shown in 12 Table 4. Generally, mixtures exhibiting more cycles to failure exhibit more cracking resistance. 13 The results from the OT test indicated that the cracking resistance of the mixture decreased with 14 the incorporation of 25% RAP. The same trend was apparent regardless if the mixture incorporated 15 WMA technology or not. Comparing the results for the mixtures with and without the WMA technology, 16 a slight improvement in the cracking resistance was noted for the 25% RAP mixture with the WMA 17 technology. Conversely a slight reduction in the in the cracking resistance was noted for the control 18 mixture. Overall, the results indicated that mixtures incorporating RAP were more susceptible to 19 cracking as compared to the control mixtures. 20 21 TABLE 4 Test Results from Overlay Test 22

Mixture Average OT

Cycles to Failure

Control 351 25% RAP 43

Control + 1% WMA 275 25% RAP + 1% WMA 64

23 24 MIXTURE LOW TEMPERATURE CRACKING - ASPHALT CONCRETE CRACKING 25 DEVICE (ACCD) 26 The low temperature cracking properties of each mixture were determined because mixtures incorporating 27 RAP are expected to exhibit increased stiffness and therefore could lead to a mixture more susceptible to 28 low temperature cracking. Therefore, all the mixtures were tested to determine their low temperature 29


cracking properties using the Asphalt Concrete Cracking Device (ACCD). This device has been validated 1 to Thermal Stress Restrained Specimen Test (TSRST) data (18). 2

The ACCD is a device that uses a circular shaped asphalt mixture specimen compacted around a 3 circular thermal stress restraining device (ACCD ring) to determine the low temperature cracking of an 4 asphalt mixture. The compacted asphalt mixture specimen and thermal stress restraining device (ACCD 5 ring) are tested together as shown in Figure 4. 6 7

ACCD Ring

8 FIGURE 4 Typical ACCD asphalt specimen and thermal stress restraining device (ACCD ring). 9

10 The basic principal of the ACCD is that as the temperature of the specimen is lowered, the asphalt 11 mixture attempts to contract. This contraction is prevented by the presence of the ACCD ring which 12 causes tensile stress in the sample and corresponding compression in the ACCD ring. This stress 13 continues to accumulate until the specimen breaks. A plot of data collected during the tests (strain 14 resulting from the thermal tensile stress on the ACCD ring versus temperature) is utilized to determine the 15 cracking temperature of the mixture. A more thorough explanation of the ACCD, corresponding 16 specimen preparation, and data analysis is available in previous research (18, 19). 17

For this study, two ACCD specimens fabricated and compacted per day. Specimens 18 incorporating WMA technology were produced at the lower mixing and compaction temperatures noted 19 previously. All specimens were aged for four hours at the compaction temperature in a loose state prior 20 to compaction. The target air voids content of the specimen was 9 ± 1% which was consistent with 21 previous research (20). The results of the testing for all the mixtures in this study are shown in Table 5. 22 According to the data, the addition of 1% WMA to the control asphalt rubber mixture improved the low 23 temperature cracking by 1.5C. The addition of the 25% RAP to the mixtures, with and without the 24


WMA technology, caused a reduction of the low temperature cracking of the asphalt rubber mixture by 1 approximately 2C. 2 3 TABLE 5 Mixture Low Temperature Cracking Properties Determined from ACCD Test 4

Mixture ACCD Cracking Temperature

Control -37.3ºC (-35.1ºF) Control + 1% WMA -38.8ºC (-37.8ºF)

25% RAP -35.0ºC (-31.0ºF) 25% RAP + 1% WMA -35.8ºC (-32.4ºF)

5 MOISTURE SUSCEPTIBILITY TESTING – HAMBURG WHEEL TRACKING DEVICE 6 The mixtures in this study were evaluated for their moisture susceptibility to determine if the addition of 7 high amounts RAP or the WMA technology had any effects on their performance. It is not known how 8 the use of asphalt rubber, RAP and WMA technology affects the mixture moisture susceptibility 9 performance. Previous research (7) has suggested that the addition of a WMA technology may increase 10 the moisture susceptibility of conventional mixtures. Therefore, in order to understand the performance 11 of these mixtures, they were subjected to moisture susceptibility testing in a Hamburg Wheel Tracking 12 Device (HWTD). 13

Testing was conducted in accordance with AASHTO T324 “Hamburg Wheel-Track Testing of 14 Compacted Hot-Mix Asphalt (HMA)” (11). The test is utilized to determine the failure susceptibility of 15 the mixture due to weakness in the aggregate structure, inadequate binder stiffness, or moisture damage 16 (11). In this test, the mixture is submerged in heated water (typically 40-50ºC) and subjected to repeated 17 loading from a 705 N steel wheel. As the steel wheel loads the specimen, the corresponding rut depth of 18 the specimen is recorded. The rut depth versus numbers of passes of the wheel is plotted to determine the 19 Stripping Inflection Point (SIP) as shown in Figure 5. The SIP gives an indication of when the test 20 specimen begins to exhibit stripping (moisture damage). 21

Gyratory specimens for this study were fabricated using the SGC to an air void level of 7.0±2.0% 22 as required by AASHTO T324. Specimens without the WMA technology were mixed at 177ºC (351ºF) 23 and then aged four hours at the compaction temperature of 154ºC (309ºF). All specimens containing the 24 WMA technology were mixed at 160ºC (320ºF) and then aged four hours at the compaction temperature 25 of 141ºC (286ºF). 26

Testing in the HWTD was conducted at a test temperature of 50ºC (122ºF). The specimens were 27 tested at a rate of 52 passes per minute after a soak time of 30 minutes at the test temperature. Testing 28 terminated at 20,000 wheel passes or until visible stripping was noted. Table 6 shows the results of the 29 moisture susceptibility testing. 30

All mixtures evaluated in this study passed the moisture susceptibility testing in the HWTD. 31 Additionally, the magnitude of the average total rut depth observed at the end of each test was less than 32 1mm (0.039 inch). 33

34 TABLE 6 HWTD Moisture Susceptibility Test Results 35

Mixture Stripping Inflection Point

Control NONE 25% RAP NONE

Control + 1% WMA NONE 25% RAP + 1% WMA NONE

NONE = Mixture passed 20,000 cycle test with no SIP. 36 37


-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000

Number of Passes

Ru

t D

ep

th (m

m)

Stripping

Inflection

Point

(SIP)

Number of

Passes to

Stripping

Inflection Point

(SIP)

Number of

Passes

Failure, N f

1 FIGURE 5 Determination of HWTD Stripping Inflection Point (SIP). 2 3 CONCLUSIONS 4 The purpose of this study was to design and evaluate asphalt rubber mixtures incorporating RAP and 5 WMA technology. The performance of these mixtures was compared to a control mixture designed with 6 asphalt rubber and new aggregates. 7 8

1. Mixtures incorporating RAP up to 25% and including a WMA technology were able to be 9 designed to meet the gradation and volumetric requirements of the ADOT section 413 specification for 10 asphalt rubber mixtures. 11 12

2. In terms of mixture stiffness, the 25% RAP and 25% RAP mixture with WMA technology 13 exhibited dynamic modulus values that were not significantly different than the corresponding control 14 mixtures. This indicated that the addition of RAP did not have negative impact on the stiffness of 15 mixtures incorporating asphalt rubber, high RAP content and WMA technology. A comparison of 16 mixtures with and without WMA technology indicated that the mixtures incorporating WMA technology 17 exhibited less stiffness than the mixture without the technology. This is likely a result of less aging due to 18 reduced mixing and compaction (aging) temperatures associated with the use of the WMA technology. 19 20

3. Cracking susceptibly testing in Overlay Test device indicated that the cracking resistance of the 21 mixture decreased with the incorporation of 25% RAP in both the mixture with and without the WMA 22 technology. Overall, the results indicated that mixtures incorporating RAP were more susceptible to 23 cracking as compared to the control mixtures. This suggested that the use of polymers or other additives 24 may be necessary to increase the intermediate temperature elasticity of these mixtures, thereby decreasing 25 the mixture cracking susceptibility. 26


1 4. The low temperature cracking results suggested that the incorporation of 25% RAP in the 2

asphalt rubber mixtures did not have negative impact on the low temperature cracking resistance of the 3 mixtures as compared to the control. Moreover, the addition of the WMA technology slightly improved 4 the low temperature cracking resistance of the binder. Therefore, this indicated the importance of 5 selecting the proper WMA technology and corresponding dose for these types of mixtures. 6 7

5. The HWTD results showed that the combination of 25% RAP, asphalt rubber, and WMA 8 technology did not have an impact on the moisture susceptibility of the mixtures. All mixtures passed the 9 HWTD test. 10

11 6. The use of RAP contents over 25% for these types of mixtures requires further study. 12

13 ACKNOWLEDGEMENTS 14 The authors would like to acknowledge Mike Nichols of Aggregate Industries and Mark Gabriel of All 15 States Asphalt, Inc. for supplying the aggregates and asphalt rubber binder for this project respectively. 16 The authors would also like to thank Chris Strack - Sonneborn, Inc. for supply the WMA technology for 17 this study. 18 19 REFERENCES 20 1. Cooper, Samuel B. Characterization of HMA Mixtures Containing High Recycled Asphalt Pavement 21 Content with Crumb Rubber Additives. Masters Thesis, Louisiana State University, December 2008. 22 23 2. Al-Qadi, I. L., S. Carpenter, G. Roberts, H. Ozer, M. Elseifi, and J. Trepanier. Determination of 24 Usable Residual Asphalt Binder in RAP. Research Report No. FHWA-ICT-09-031. Federal Highway 25 Administration, U.S. Department of Transportation and Illinois Department of Transportation, January 26 2009. 27 28 3. Daniel, J.S. and G.R. Chehab. Use of RAP Mixtures in the Mechanistic Empirical Pavement Design 29 Guide. In Transportation Research Board 2008 Annual Meeting CD-ROM, Transportation Research 30 Board of the National Academies, Washington, D.C., 2008. 31 32 4. Daniel, J.S. and A. Lachance. Mechanistic and Volumetric Properties of Asphalt Mixtures with RAP. 33 In Transportation Research Board 2005 Annual Meeting CD-ROM, Transportation Research Board of the 34 National Academies, Washington, D.C., 2005. 35 36 5. Bonaquist, R. Evaluation of Hot-Mix Asphalt Mixtures Containing Recycled or Waste Product 37 Materials Using Performance Testing. Report for Valley Forge Laboratories Inc. May 25, 2005. 38 39 6. Hurley, G.C. and B.D. Prowell. Evaluation of Potential Processes for Use in Warm Mix Asphalt. 40 Journal of the Association of Asphalt Paving Technologists, Vol. 75, 2006, pp.41-90. 41 42 7. Austerman, A.J., W.S. Mogawer, and R. Bonaquist. “Investigation of the Influence of Warm Mix 43 Asphalt Additive Dose on the Workability, Cracking Susceptibility, and Moisture Susceptibility of 44 Asphalt Mixtures Containing Reclaimed Asphalt Pavement.” In Canadian Technical Asphalt Association 45 (CTAA) Proceedings. Moncton - New Brunswick, pg. 51-71, November 2009. 46 47 8. Li, X., M.O. Marasteanu, R.C. Williams and T.R. Clyne. Effect of RAP (Proportion and Type) and 48 Binder Grade on Properties of Asphalt Mixtures. In Transportation Research Board 2008 Annual Meeting 49 CD-ROM, Transportation Research Board of the National Academies, Washington, D.C., 2008. 50 51


9. McDaniel, R.S., A. Shah, G.A. Huber, and V. L. Gallivan. Investigation of Properties of Plant-1 Produced RAP Mixtures. In Transportation Research Board 2007 Annual Meeting CD-ROM, 2 Transportation Research Board of the National Academies, Washington, D.C., 2007. 3 4 10. American Society for Testing and Materials (ASTM). Annual Book of ASTM Standard. ASTM 5 International, West Conshohocken, PA, Section Four - Construction, Volume 04.03, 2008. 6 7 11. American Association of State Highway and Transportation Officials. Standard Specifications for 8 Transportation Materials and Methods of Sampling and Testing. American Association of State Highway 9 and Transportation Officials (AASHTO).Washington, D.C. 28th Edition. 2008. 10 11 12. Arizona Department of Transportation (ADOT). Section 413 Asphaltic Concrete (Asphalt-Rubber). 12 Standard Specifications, 2000. 13 http://www.azdot.gov/Highways/ConstGrp/Contractors/PDF/2000_Standard_Spec/Sec401_417.pdf 14

Accessed July 15th, 2010. 15 16 13. American Association of State Highway and Transportation Officials. 2008 AASHTO Provisional 17 Standards. American Association of State Highway and Transportation Officials (AASHTO).Washington, 18 D.C. June 2008 Edition. 19

20 14. Bonaquist, R. Refining the Simple Performance Tester for Use in Routine Practice. National 21 Cooperative Highway Research Program (NCHRP) Report 614, Transportation Research Board of the 22 National Academies, Washington, D.C., 2008. 23 24 15. Texas Department of Transportation (TxDOT). Test Procedure for Overlay Test. TxDOT Designation 25 Tex-248-F, January 2009. 26 ftp://ftp.dot.state.tx.us/pub/txdot-info/cst/TMS/200-F_series/pdfs/bit248.pdf 27

Accessed July 15th, 2010. 28 29 16. Zhou, F., S. Hu, T. Scullion, D. Chen, X. Qi, and G. Carlos. Development and Verification of the 30 Overlay Tester Based Fatigue Cracking Prediction Approach. Journal of the Association of Asphalt 31 Paving Technologists, Vol. 76, 2007, pp. 627-662. 32

17. Zhou, F., S. Hu, and T. Scullion. Overlay Tester: A Simple Performance Test for Fatigue Cracking. In 33 Transportation Research Record: Journal of the Transportation Research Board, No. 2001, 34 Transportation Research Board of the National Academies, Washington, D.C., 2007, pp. 1-8. 35

18. Kim, S., S. Sargand and A. Wargo. A Simple Test Procedure for Evaluating Low Temperature Crack 36 Resistance of Asphalt Concrete. Publication FHWA/OH-2009/5. Ohio Department of Transportation, 37 November 2009. 38 39 19. Kim, S., A. Wargo, and D. Powers. Asphalt Concrete Cracking Device to Evaluate Low Temperature 40 Performance of HMA. Journal of the Association of Asphalt Paving Technologists, Vol. 79, 2010. 41 42

Mogawer, Austerman, & Roussel 1 · Dr. Walaa S. Mogawer, P.E. – Corresponding Author . Civil and...

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